Lets face it, BTC is going to die sooner or later for GPU miners. As a few have said, anything SHA based is pretty much stuffed.
Then scrypt will face similar problems with the increase of GPU miners switching, difficulty will increase making it harder for small time miners to stay in. Only the heavy hitters will stay afloat.
The surprise for scrypt miners will come when mining scrypt is not profitable either. Who would trade ASIC earned BTC for GPU earned LTC at an effective loss? Yes I do believe the LTC economy is just an accessory to the BTC economy and can't stand up on its own right.
There's always the possibility of scrypt-based litecoin being a healthy and/or more stable cryptocurrency than bitcoin...
What if:
- Bitcoin fails because of internal political disputes among devs and/or userbase, or perhaps a critical flaw is discovered which scrypt is not affected by
- Litecoin thrives because of adoption because of some arbitrary organization, social and/or political advocacy, etc. etc. etc.
Either scenario seems plausible to me... Or maybe they could just coexist like VHS and DVD, or sega dreamcast and sony playstation.